Those are topics the person has posted in. But the list is not necessarily in the order that the person posts in, the list is sorted by "most recent post made", whether that recent post was made by the member in question or not. Thus, the profile of a member who stopped posting years ago might show one of the large, old megathreads as a "recent topic".
There isn't any way to follow a particular person's posts, sorry.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis